This invention relates to blow guns which are used for example in manufacturing processes to clear metal shavings or swarf from drilled passages. Conveniently the gun is adapted to be connected to a source of compressed air and is arranged to be switched between "on" and "off" positions. It has been found that guns of this kind can be dangerous in that if the outlet nozzle contacts the operator's skin when the gun is "on" then high pressure air, for example of pressures of 100 pounds per square inch, may penetrate the skin.